DUP(2) Linux Programmer's Manual DUP(2)
NAME
dup, dup2 - duplicate a file descriptor
SYNOPSIS#include<unistd.h>intdup(intoldfd);intdup2(intoldfd,intnewfd);DESCRIPTIONdup and dup2 create a copy of the file descriptor oldfd.
The old and new descriptors may be used interchangeably.
They share locks, file position pointers and flags; for
example, if the file position is modified by using lseek
on one of the descriptors, the position is also changed
for the other.
The two descriptors do not share the close-on-exec flag,
however.
dup uses the lowest-numbered unused descriptor for the new
descriptor.
dup2 makes newfd be the copy of oldfd, closing newfd first
if necessary.
RETURNVALUEdup and dup2 return the new descriptor, or -1 if an error
occurred (in which case, errno is set appropriately).
ERRORSEBADFoldfd isn't an open file descriptor, or newfd is
out of the allowed range for file descriptors.
EMFILE The process already has the maximum number of file
descriptors open and tried to open a new one.
WARNING
The error returned by dup2 is different to that returned
by fcntl(...,F_DUPFD,...) when newfd is out of range. On
some systems dup2 also sometimes returns EINVAL like
F_DUPFD.
CONFORMINGTO
SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4 documents addi-
tional EINTR and ENOLINK error conditions. POSIX.1 adds
EINTR.
SEEALSOfcntl (2), open (2), close (2).
Linux 1.1.46 21 August 1994 1